1. Field of the Invention
The present invention relates to a semiconductor pressure sensor controlled based on a pressure medium detection signal, and relates more specifically to a semiconductor pressure sensor for use in, for example, an automotive transmission control system.
2. Description of the Related Art
Semiconductor pressure sensors of a type related to the present invention typically detect the pressure of a pressure medium based on the magnitude of distortion in a semiconductor body. Semiconductor pressure sensors of this type are taught, for example, in Japanese Patent Laid-Open Publications Nos. 60-73325 (1985), 62-266429 (1987), and 6-3211 (1994). An exemplary conventional semiconductor pressure sensor related to the present invention is shown in FIG. 4 and FIG. 5 and described below.
This semiconductor pressure sensor 50 has a sensor element 53 comprising silicon single crystal sensor chip 51 and a pedestal 52 on which the sensor chip 51 is affixed, and a plate 54 to which the pedestal 52 of the sensor element 53 is bonded.
The sensor element 53 has an anodically bonded structure with three layers, silicon, glass, and silicon. A diaphragm (not shown in the figures) is formed in the sensor chip 51 by anistropic etching of the silicon. A pressure opening 55 is also formed through the plate 54 and pedestal 52 so that pressure from the pressure medium passes through this pressure opening 55 and is applied to the diaphragm.
A pressure medium detection signal detected by the sensor chip 51 is passed to a level adjustment circuit board 56 for adjustment and amplification to a level required for system processing. The level adjustment circuit board 56 is mounted on the plate 54, and is connected to the sensor chip 51 by wire 57.
The semiconductor pressure sensor 50 is mounted as described below to a mounting part 59 provided at a particular pressure detection point of a system-side body 58. More specifically, the plate 54 of the semiconductor pressure sensor 50 is fit to the mounting part 59, and a lip 61 around the edge of the mounting part 59 is crimped to the plate 54, thereby fixing the plate 54 in the mounting part 59. A system circuit board 62 mounted on the system-side body 58 is connected to the level adjustment circuit board 56 by wire 63.
Because the sensor element 53 of this semiconductor pressure sensor 50 is directly connected to the plate 54, thermal stress from the system-side body 58 on the sensor element 53 passes the plate 54 and is applied directly to the pedestal 52 of the sensor element 53. This means that much thermal stress is applied from the system-side body 58 to the sensor element 53 in this exemplary conventional semiconductor pressure sensor 50.
Furthermore, the inside wall of the support member supporting the outside edge of the diaphragm is formed at an angle to the bonding surface of the sensor chip 51 and pedestal 52 because the diaphragm of the sensor chip 51 is formed by anistropic etching.
When thermal stress is repeatedly applied from the system-side body 58 to a conventional semiconductor pressure sensor 50 thus comprised, stress concentration repeatedly develops in particular areas, such as the middle of each side of the rectangular diaphragm part of the sensor chip 51, and the bond between the sensor chip 51 and pedestal 52. Such stress concentration reduces the strength of the sensor chip 51, and lowers the pressure resistance.
As noted above, this conventional semiconductor pressure sensor 50 is mounted to the mounting part 59 by fitting plate 54 to the mounting part 59 of system-side body 58, and crimping the lip 61 around the mounting part 59 to the plate 54. It is therefore difficult to maintain an airtight seal between the plate 54 and lip 61 in a conventional semiconductor pressure sensor 50 thus comprised. As a result, part of the pressure applied to the sensor chip 51 of the sensor element 53 escapes between the system-side body 58 and plate 54 from the lip 61, and the accuracy of pressure detection by the sensor element 53 therefore drops.